Method and device for managing user information

ABSTRACT

Embodiments of the present disclosure relate to a method for managing user information in a SIP network and a device thereof. The method comprises: initiating a restart timer after a SIP access gateway restarts; within an expiration period of the restart timer, sending a heartbeat reply message to the network element in response to a heartbeat message from a network element, the reply message including the time when the SIP access gateway restarts. If a difference between the time when the SIP access gateway restarts and a current time is less than a time interval between heartbeat messages, the network element sends a registration request to the SIP access gateway, where the registration request includes user information of all users represented by the network element. It is further disclosed a device implementing the method discussed above.

FIELD

Embodiments of the present disclosure generally relate to communicationtechnologies, and more particularly, to a method and device for managinguser information.

BACKGROUND

In some remote or scarcely populated areas, such as hamlets, islands andthe like, there are generally only deployed SIP access gateways. TheseSIP access gateways communicate with SIP application servers which aredeployed in towns or on the mainland and provide a voice service or amost value-added service for users within the coverage of these SIPaccess gateways. However, once the communication between the SIP accessgateways and the SIP application server breaks down, for example due tothe fiber line interruption caused by an earthquake, the users withinthe coverage of the SIP access gateways cannot communicate with eachother, which means that the “local” communication within the SIP accessgateways is also disconnected.

Lots of telecommunication customers intend to communicate with eachother in these isolated areas in case that the communication between SIPaccess gateways and SIP application servers breaks down. Therefore,enhanced SIP access gateways appears, which can provide a basicone-to-one call service and forward SIP messages in a stateless way,which means that the enhanced SIP access gateways do not record statesof calls. Such an enhanced SIP access gateway may employ its own simplecall application processing function to provide the basic phone callservice for terminal users, user agents and further non-enhanced accessgateways within the local network. Once launched, the enhanced SIPaccess gateways are well received by the customers with an increasingnumber of deployments.

Since the enhanced SIP access gateways do not have high servicerequirements and larger deployments, the customers expect that the SIPaccess gateways may be easily implemented with a low cost. Therefore,the enhanced SIP access gateways do not configure user information inadvance and obtain and save user information by registration learning,that is, user registration. However, after the SIP access gatewaysrestart for some reasons, they loses all their user information. Therestart occurs in a short period, while the time duration to triggeruser re-registration is quite long (generally 1800˜3600 seconds).Therefore, between the restart of the SIP access gateway and thecompletion of all user re-registration, many users will not receivecalls due to loss of user information. As a result, the users within thecoverage of the SIP access gateway cannot communicate normally.

Therefore, there is a need to provide a method for solving the problemof a communication failure due to the restart of the enhanced SIP accessgateway.

SUMMARY

Generally, the embodiments of the present disclosure present a methodand device for managing user information in a SIP network.

In a first aspect of the present disclosure, there is provided a methodof managing user information in a SIP access gateway, where the methodcomprises: in response to the SIP access gateway restarting, initiatinga restart timer; within an expiration period of the restart timer,sending a heartbeat reply message to a network element in response to aheartbeat message from the network element, the reply message includinga time when the SIP access gateway restarts.

In some embodiments, the network element is a terminal user, a useragent or a further SIP access gateway.

In some embodiments, the heartbeat message is a REGISTER message or anOPTIONS message.

In a second aspect of the present disclosure, there is provided a methodof managing user information in a network element of a SIP network. Themethod comprises: receiving from a SIP access gateway a heartbeat replymessage, the heartbeat reply message includes the time when the SIPaccess gateway restarts; if a difference between the time when the SIPaccess gateway restarts and a current time is less than a time intervalbetween heartbeat messages, sending to the SIP access gateway aregistration request, where the registration request includes userinformation of a user represented by the network element.

In some embodiments, the network element is a terminal user, a useragent or a further SIP access gateway.

In some embodiments, the heartbeat message is a REGISTER message or anOPTIONS message.

In a third aspect of the present disclosure, there is provided anapparatus for managing user information in a SIP access gateway, wherethe apparatus comprises: timer initiating module configured to initiatea restart timer in response to the SIP access gateway restarting; firstsending module configured to, within an expiration period of the restarttimer, send a heartbeat reply message to a network element in responseto a heartbeat message from the network element, the reply messageincluding the time when the SIP access gateway restarts.

In some embodiments, the network element is a terminal user, a useragent or a further SIP access gateway.

In some embodiments, the heartbeat message is a REGISTER message or anOPTIONS message.

In a fourth aspect of the present disclosure, there is provided anapparatus for managing user information in a network element of a SIPnetwork, where the apparatus comprises: receiving module configured toreceive a heartbeat reply message from a SIP access gateway, where theheart replay message includes a time when the SIP access gatewayrestarts; second sending module configured to send a registrationrequest to the SIP access gateway if a difference between the time whenthe SIP access gateway restarts and a current time is less than a timeinterval between heartbeat messages, where the registration requestincludes user information of a user represented by the network element.

In some embodiments, the network element is a terminal user, a useragent or a further SIP access gateway.

In some embodiments, the heartbeat message is a REGISTER message or anOPTIONS message.

In the embodiments of the present disclosure, after the SIP accessgateway with a simple call application processing function restarts, itwill include its restart time in the replies to all the receivedheartbeat messages Upon the reception of the replies, the user agent,the terminal user or a further SIP access gateway re-registers accordingto a determination. Typically, the time intervals between heartbeatmessages are short, such as 60˜90 seconds. With the method, after theSIP access gateway restarts, it can re-obtain user information of allusers within its coverage, so that the time period in which the voiceservice is lost will be greatly shortened.

It should be appreciated the description in the SUMMARY are not intendedto limit essential or important features of the embodiments of thepresent disclosure or used to limit the scope of the present disclosure.Other features of the present disclosure will become easier tounderstand from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features, advantages and aspects of variousembodiments of the present disclosure will become apparent from thefollowing detailed illustration, when taken in conjunction with theaccompanying drawings in which the same or similar reference signsdenote the same or similar elements, in which:

FIG. 1 shows an example network architecture in which one embodiment ofthe present disclosure may be implemented;

FIG. 2 shows a schematic diagram of the process of restart of a SIPaccess gateway in the prior art;

FIG. 3 shows a schematic diagram of the process for managing userinformation according to one embodiment of the present disclosure;

FIG. 4 shows a block diagram of an apparatus for managing userinformation according to one embodiment of the present disclosure; and

FIG. 5 shows a block diagram of an apparatus for managing userinformation according to another embodiment of the present disclosure.

The same or similar reference numerals denote the same or similarelements throughout the figures.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure will be described in more detailwith reference to the accompanying drawings, in which some embodimentsof the present disclosure have been illustrated. However, the presentdisclosure can be implemented in various manners, and thus should not beconstrued to be limited to the embodiments disclosed herein. On thecontrary, those embodiments are provided for the thorough and completeunderstanding of the present disclosure. It should be appreciated thatthe accompanying drawings and embodiments of the present disclosure aremerely for the illustration purpose, rather than limiting the scope ofthe present disclosure.

The terms “comprise”, “include” and their variants used here are to beread as open terms that mean “include, but is not limited to”. The term“based on” is to be read as “based at least in part on”. The term “oneembodiment” is to be read as “at least one embodiment”; the term“another embodiment” is to be read as “at least one other embodiment”.Definitions of other terms will be presented in description as below.

A more detailed description is presented below to the present inventionwith reference to the accompanying drawings.

FIG. 1 shows an example network architecture in which an embodiment ofthe present disclosure may be implemented. In this embodiment, a SIPaccess gateway 101 is connected to a SIP server 102. The user agents,namely UA103 and UA104, terminal user UE105 as well as a SIP accessgateway 106 access a network via the SIP access gateway 101.

As described above, when the SIP access gateway 101 is disconnected withthe SIP server 102, in order to ensure users within the coverage of theSIP access gateway 101 can make “local” calls, the SIP access gateway101 can provide basic call service and forward SIP messages in astateless way, that is the SIP access gateway 101 does not record statesof calls. The SIP access gateway 101 may employ its own simple callapplication processing function to provide the basic phone call servicefor the user agents UA103 and UA104, the terminal user UE105 and thenon-enhanced SIP access gateway 106 within the local network. The SIPaccess gateway 101 does not configure user information in advance, andobtains and saves user information only by registration learning, thatis, user registration.

It should be appreciated that the type and number of devices and/orelements shown in FIG. 1 are merely for the illustration purpose and notlimiting. Generally, the network architecture may comprise a device suchas a gateway, which is not shown in FIG. 1 for the simplicity.

FIG. 2 shows a schematic diagram of the process of restart of a SIPaccess gateway in the prior art. The process will be described in detailwith reference to FIG. 1. In this embodiment, the communication betweenthe SIP access gateway 101 and the SIP server 102 breaks down.

First, the user agent UA103 sends (S201) to the SIP access gateway 101 aregistration message, such as a REGISTER message, which includes userinformation of a user represented by the user agent UA103. When the useragent UA103 represents multiple users, the user agent UA103 will sendmultiple registration messages to the SIP access gateway 101.

Upon reception of the above registration message, the SIP access gateway101 saves the above user information. Subsequently, the SIP accessgateway 101 sends (S202) 200 OK to the user agent UA103. Upon receipt ofthe reply message of 200 OK, the user agent UA103 initiates (S203) aregistration timer.

Later at a time point, the SIP access gateway 101 restarts (S203) due tosome reasons. After the SIP access gateway 101 restarts, it loses alluser information saved thereon. At this point, many users will notreceive calls due to loss of user information.

After a registration timer of the user agent UA103 expires (S205), theuser agent UA103 re-registers with the SIP access gateway 101, that is,the user agent UA103 sends (S206) to the SIP access gateway 101 one ormore registration messages, such as REGISTER messages for example. Theregistration messages include user information of a user represented bythe user agent UA103. Upon reception of the user information, the SIPaccess gateway 101 will save the user information. After all user agentswithin the coverage of the SIP access gateway 101 completere-registration, all user information on the SIP access gateway 101 isrestored, and users within the coverage of the SIP access gateway 101may restore “local” communication.

It can be seen that in the prior art, given the communication betweenthe SIP access gateway 101 and the SIP server 102 breaking down, if theSIP access gateway 101 restarts, in a time period between the restart ofthe SIP access gateway 101 and the completion of user agentre-registration, many users within the coverage of the SIP accessgateway 101 will not receive calls due to loss of user information. Thisis exactly the problem to be solved by the present disclosure.

FIG. 3 shows a schematic diagram of the process for managing userinformation according to one embodiment of the disclosure. The processwill be described in detail with reference to FIG. 1.

In the SIP network, a network element connected to the SIP accessgateway periodically sends to the SIP access gateway a heartbeat messagefor monitoring whether the communication between the user agent and theSIP access gateway is normal. As shown in FIG. 3, the user agent UA103sends (S301) a heartbeat message to the SIP access gateway 101, and theheartbeat message is a REGISTER message or an OPTIONS message. Upon thereception of the message, the SIP access gateway 101 sends (S302) areply message of 200 OK to the user agent UA103.

The user agent UA103 sends (S303) to the SIP access gateway 101 aregistration message, such as a REGISTER message for example, whichincludes user information of a user represented by the user agent UA103.When the user agent UA103 represents multiple users, the user agentUA103 will send multiple registration messages to the SIP access gateway101. The SIP access gateway 101, upon reception of the user information,saves the user information and then sends 200 OK to the user agentUA103. Upon receipt of the 200 OK, the user agent UA103 initiates (S305)a registration timer.

When the time interval between heartbeat messages is reached, the useragent UA103 will re-send (S306) a heartbeat message to the SIP accessgateway 101, and the heartbeat message is a REGISTER message or anOPTIONS message. Upon reception of the heartbeat message, the SIP accessgateway 101 sends (S307) a reply message of 200 OK to the user agentUA103.

The SIP access gateway 101 restarts (S308) due to some reasons, and inthe meanwhile initiates (S309) a restart timer.

After the SIP access gateway 101 restarts, when the time intervalbetween heartbeat messages is reached again, the user agent UA103 willre-send (S309) a heartbeat message to the SIP access gateway 101. Theheartbeat message is a REGISTER or an OPTIONS message. Upon receipt ofthe message, the SIP access gateway 101 sends (S310) the reply messageof 200 OK to the user agent UA103, and the reply message includes thetime when the SIP access gateway 101 restarts. The restart time may be arelative time or an absolute time. For example, the restart time may be10 minutes ago, and the restart time may be 22:05, etc.

Those skilled in the art will appreciate that the time when the SIPaccess gateway 101 restarts may be included in the heartbeat message invarious suitable ways. For example, the time when the SIP access gateway101 restarts may be included in a WARNING header of a SIP message.

Upon reception (S310) of the above heartbeat reply message, the useragent UA103 reads the time when the SIP access gateway 101 restarts, anddetermines (S311) whether a difference between the restart time and acurrent time is less than the time interval between heartbeat messages.

If the difference between the restart time and the current time is lessthan the time interval between heartbeat messages, which means userinformation of the user agent UA103 in the SIP access gateway 101 hasbeen lost, the user agent UA103 will re-register. The user agent UA103re-sends (S312) to the SIP access gateway 101 one or more registrationmessages, such as REGISTER messages for example, which include userinformation of a user represented by the user agent UA103. Upon thereception of the message, the SIP access gateway 101 saves the aboveuser information, and then sends the 200 OK to the user agent UA103. Insome embodiments, the SIP access gateway 101 cannot determine whetherthe registration message is used for registration or for heartbeatdetection; and therefore the SIP access gateway 101 will still includein the message of 200 OK the time when the SIP access gateway 101restarts.

After the restart timer on the SIP access gateway 101 expires (S314),the SIP access gateway 101 considers it has obtained the userinformation of the user agent UA103. Therefore, when a heartbeat messageof the user agent UA103 is received (S315) again, the user agent UA103does not need to re-register. Upon reception (S315) of the heartbeatmessage, the SIP access gateway 101 sends (S316) to the user agent UA103a reply message of 200 OK, which no longer includes the time when theSIP access gateway 101 restarts.

It can be seen that in the present invention, the SIP access gateway101, after the restarting, will include its restart time in replies toall received heartbeat messages. The user agent, the terminal user or afurther SIP access gateway will re-register according to a determinationresult. Upon reception of the reply. Generally, the time intervalsbetween heartbeat messages are relatively short, such as 60˜90 seconds.With the method, after the restarting, the SIP access gateway 101 canre-obtain user information of all users within its coverage in a shorttime, so that the time for which voice service is lost will besignificantly shortened.

FIG. 4 shows a block diagram of an apparatus for managing userinformation according to one embodiment of the present invention. Itwill be appreciated that the apparatus 400 may be implemented at a SIPaccess gateway (such as the SIP access gateway 101). The apparatus 400comprises: timer initiating module 401 and first sending module 402.

With reference to FIGS. 1 and 3, a detailed description is presentedbelow to the working process of the apparatus 400.

The SIP access gateway 101 restarts due to some reasons, and in themeanwhile the timer initiating module 401 initiates a restart timer.

After the SIP access gateway 101 restarts, upon the SIP access gateway101 receiving a heartbeat message (such as REGISTER message or OPTIONSmessage) from some network element, the first sending module 402 sends aheartbeat reply message to the network element. The reply messageincludes the time when the SIP access gateway 101 restarts. The restarttime may be a relative time or an absolute time. For example, therestart time may be 10 minutes ago, and the restart time may be 22:05,etc. The network element may be the user agent UA103, the user agentUA104, the terminal user UE105, or the non-enhanced SIP access gateway106.

Those skilled in the art may appreciate that the time when the SIPaccess gateway 101 restarts may be included in the heartbeat replymessage in various suitable ways. For example, the time may be includedin a WARNING header of a SIP message.

Subsequently, Upon reception of one or more registration messages aboutre-registration of the network element, the SIP access gateway 101 savesuser information of a user represented by the network element.

After the restart timer on the SIP access gateway 101 expires, the SIPaccess gateway 101 considers it has obtained user information of allusers represented by the network element. Therefore, when a heartbeatmessage of the network element is received again, a reply message isdirectly sent to the network element without a need of re-registration,which means the reply message no longer includes the time when the SIPaccess gateway 101 restarts.

FIG. 5 shows a block diagram of an apparatus for managing userinformation according to one embodiment of the present invention. Itwill be appreciated that the apparatus 500 may be implemented at a useragent (such as the user agent UA103 or the user agent UA104), a terminaluser (the terminal user UE105) or a SIP access gateway (a furthernon-enhanced SIP access gateway 106). The apparatus 500 comprises:receiving module 501 and second sending module 502.

With reference to FIGS. 1 and 3, a detailed description is presentedbelow to the working process of the apparatus 500.

First, the receiving module 501 in the user agent UA103 receives from aSIP access gateway a heartbeat reply message, such as 200 OK. Theheartbeat reply message includes the time when the SIP access gateway101 restarts.

Next, the user agent UA103 determines a difference between the restarttime and a current time is less than a time interval between heartbeatmessages. The heartbeat message may be a REGISTER message or an OPTIONSmessage. If the difference between the restart time and the current timeis less than the time interval between heartbeat messages, which meansuser information of the user agent UA103 on the SIP access gateway 101has been lost, the user agent UA103 will re-register on behalf of allusers thereon. The second sending module 502 re-sends (S312) to the SIPaccess gateway 101 a registration message, such as REGISTER message. Theregistration message includes user information of a user represented bythe user agent UA103. If the user agent UA103 represents multiple users,the second sending module 502 will send multiple registration messagesto the SIP access gateway 101.

Generally, various embodiments of the present disclosure may beimplemented in hardware or special purpose circuit, software, logic orany combination thereof. Some aspects may be implemented in hardware,while other aspects may be implemented in firmware or software which maybe executed by a controller, microprocessor or other computing device.While various aspects of embodiments of the present disclosure areillustrated and described as block diagrams, flowcharts, or using someother diagrammatic representation, it will be appreciated that theblocks, apparatus, systems, techniques or methods described herein maybe implemented in, as non-limiting examples, hardware, software,firmware, special purpose circuits or logic, general purpose hardware orcontroller or other computing devices, or some combination thereof.

For example, embodiments of the present disclosure can be described inthe general context of machine-executable instructions, such as thoseincluded in program modules, being executed in a device on a target realor virtual processor. Generally, program modules include routines,programs, libraries, objects, classes, components, data structures, orthe like that perform particular tasks or implement particular abstractdata types. The functionality of the program modules may be combined ordivided between program modules as desired in various embodiments.Machine-executable instructions for program modules may be executedwithin a local or distributed device. In a distributed device, programmodules may be located in both local and remote storage media.

Program code for carrying out methods of the present disclosure may bewritten in any combination of one or more programming languages. Theseprogram codes may be provided to a processor or controller of a generalpurpose computer, special purpose computer, or other programmable dataprocessing apparatus, such that the program codes, when executed by theprocessor or controller, cause the functions/operations specified in theflowcharts and/or block diagrams to be implemented. The program code mayexecute entirely on a machine, partly on the machine, as a stand-alonesoftware package, partly on the machine and partly on a remote machineor entirely on the remote machine or server.

In the context of this disclosure, a machine readable medium may be anytangible medium that may contain, or store a program for use by or inconnection with an instruction execution system, apparatus, or device.The machine readable medium may be a machine readable signal medium or amachine readable storage medium. A machine readable medium may includebut is not limited to an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, apparatus, or device, or any suitablecombination of the foregoing. More specific examples of the machinereadable storage medium would include an electrical connection havingone or more wires, a portable computer diskette, a hard disk, a randomaccess memory (RAM), a read-only memory (ROM), an erasable programmableread-only memory (EPROM or Flash memory), an optical storage device, amagnetic storage device, or any suitable combination thereof.

Further, while operations are depicted in a particular order, it shouldnot be appreciated as requiring that such operations be performed in theparticular order shown or in sequential order, or that all illustratedoperations be performed, to achieve desirable results. In certaincircumstances, multitasking and parallel processing may be advantageous.Likewise, while several specific implementation details are contained inthe above discussions, these should not be construed as limitations onthe scope of the present disclosure, but rather as descriptions offeatures that may be specific to particular embodiments. Certainfeatures that are described in the context of separate embodiments mayalso be implemented in combination in a single embodiment. Rather,various features that are described in the context of a singleembodiment may also be implemented in multiple embodiments separately orin any suitable sub-combination.

Although the subject matter has been described in a language that isspecific to structural features and/or method actions, it is to beappreciated the subject matter defined in the appended claims is notlimited to the specific features or actions described above. Rather, theabove-described specific features and actions are disclosed as anexample of implementing the claims.

I claim:
 1. A method of managing user information in a SIP accessgateway, the method comprising: in response to the SIP access gatewayrestarting, initiating a restart timer at the SIP access gateway; andwithin an expiration period of the restart timer, sending a heartbeatreply message from the SIP access gateway to a network element inresponse to a heartbeat message from the network element, the heartbeatreply message including a time indicating when the SIP access gatewayrestarted.
 2. The method according to claim 1, wherein the networkelement is a terminal user, a user agent or a further SIP accessgateway.
 3. The method according to claim 1, wherein the heartbeatmessage is a REGISTER message or an OPTIONS message.
 4. The methodaccording to claim 1, further comprising: within the expiration periodof the restart timer, receiving the heartbeat message from the networkelement at the SIP access gateway.
 5. The method according to claim 1,further comprising: receiving a registration message from the networkelement at the SIP access gateway to re-register the SIP access gatewayafter the SIP access gateway restarted, the registration messageincluding user information of a user represented by the network element;and sending a registration reply message from the SIP access gateway tothe network element in response to the registration message, theregistration reply message including the time indicating when the SIPaccess gateway restarted.
 6. A method of managing user information in anetwork element of a SIP network, the method comprising: receiving aheartbeat reply message from a SIP access gateway at the networkelement, the heart reply message including a time indicating when theSIP access gateway restarted; and if a difference between the time whenthe SIP access gateway restarted and a current time is less than a timeinterval between heartbeat messages sent by the network element, sendinga registration request from the network element to the SIP accessgateway, the registration request including user information of a userrepresented by the network element.
 7. The method according to claim 6,wherein the network element is a terminal user, a user agent or afurther SIP access gateway.
 8. The method according to claim 6, whereinthe heartbeat message is a REGISTER message or an OPTIONS message. 9.The method according to claim 6, further comprising: sending theheartbeat message from the network element to the SIP access gateway.10. The method according to claim 6, further comprising: receiving aregistration reply message from the SIP access gateway at the networkelement, the registration reply message including the time indicatingwhen the SIP access gateway restarted.
 11. An apparatus for managinguser information in a SIP access gateway, the apparatus comprising: atleast one processor; and at least one memory including computer programcode; wherein the at least one memory and the computer program code areconfigured to, with the at least one processor, cause the SIP accessgateway to initiate a restart timer in response to the SIP accessgateway restarting; wherein the at least one memory and the computerprogram code are configured to, with the at least processor, within anexpiration period of the restart timer, cause the SIP access gateway tosend a heartbeat reply message to a network element in response to aheartbeat message from the network element, the heartbeat reply messageincluding a time indicating when the SIP access gateway restarted. 12.The apparatus according to claim 11, wherein the network element is aterminal user, a user agent or a further SIP access gateway.
 13. Theapparatus according to claim 11, wherein the heartbeat message is aREGISTER message or an OPTIONS message.
 14. The apparatus according toclaim 11, wherein the at least one memory and the computer program codeare configured to, within the expiration period of the restart timer,cause the SIP access gateway to receive the heartbeat message from thenetwork element.
 15. The apparatus according to claim 11, wherein the atleast one memory and the computer program code are configured to causethe SIP access gateway to receive a registration message from thenetwork element to re-register the SIP access gateway after the SIPaccess gateway restarted, the registration message including userinformation of a user represented by the network element; wherein the atleast one memory and the computer program code are configured to causethe SIP access gateway to send a registration reply message to thenetwork element in response to the registration message, theregistration reply message including the time indicating when the SIPaccess gateway restarted.
 16. An apparatus of managing user informationin network element of a SIP network, the apparatus comprising: at leastone processor; and at least one memory including computer program code;wherein the at least one memory and the computer program code areconfigured to, with the at least one processor, cause the networkelement to receive a heartbeat reply message from a SIP access gateway,the heartbeat reply message including a time indicating when the SIPaccess gateway restarted; wherein the at least one memory and thecomputer program code are configured, with the at least processor, causethe network element to send a registration request to the SIP accessgateway if a difference between the time when the SIP access gatewayrestarted and a current time is less than a time interval betweenheartbeat messages sent by the network element, the registration requestincluding user information of a user represented by the network element.17. The apparatus according to claim 16, wherein the network element isa terminal user, a user agent or a further SIP access gateway.
 18. Theapparatus according to claim 16, wherein the heartbeat message is aREGISTER message or an OPTIONS message.
 19. The apparatus according toclaim 16, wherein the at least one memory and the computer program codeare configured to, within the expiration period of the restart timer,cause the network element to send the heartbeat message to the SIPaccess gateway.
 20. The apparatus according to claim 16, wherein the atleast one memory and the computer program code are configured to causethe network element to receive a registration reply message from the SIPaccess gateway, the registration reply message including the timeindicating when the SIP access gateway restarted.